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Understanding Moles: Definition, Significance, and Calculations in Chemistry

A mole is a fundamental unit in chemistry, representing 6.02 x 10²³ entities, known as Avogadro's number. To grasp its significance, consider that this quantity equates to various real-world examples, such as the number of blood cells in all humans or the volume of watermelon seeds in a large melon. The mole facilitates conversion between mass and number of particles, making it essential for chemical reactions. This guide covers historical insights, calculating molar mass for substances, and practical examples, enhancing your comprehension of this crucial concept.

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Understanding Moles: Definition, Significance, and Calculations in Chemistry

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  1. WHAT IS A MOLE? • 602214199000000000000000 • 6.02 x 1023

  2. Mole Facts • 6.02 X 1023  Pennies: Would make at least 7 stacks that would reach the moon. • 6.02 X 1023 Watermelon Seeds: Would be found inside a melon slightly larger than the moon. • 6.02 X 1023  Blood Cells: Would be more than the total number of blood cells found in every human on earth. • 1 Liter bottle of Water contains 55.5 moles H20

  3. A Brief History… • Amadeo Avogadro was an Italian physics professor who proposed in 1811 that equal volumes of different gases at the same temperature contain equal numbers of molecules • Josef Loschmidt, an Austrian high school teacher,in 1865, calculated the number of molecules in one cm3 of gaseous substance to be somewhere around 2.6 x 1019 • J.Perrin (1908) estimated the value to be between 6.5 x 1023 and 6.9 x 1023 • Rutherford and Geiger used radioactive methods: 6.2 x 1023 • The best modern values for what we now call "Avogadro's Number" are the result of the x-ray diffraction measurement of lattice distances in metals and salts.

  4. Definition of a Mole • The amount of atoms in 12.0 grams of Carbon 12 (6.02 x 1023 atoms known as Avogadro’s number). • A sample of any element with a mass equal to that element's atomic weight (in grams) will contain precisely one mole of atoms (6.02 x 1023 atoms).

  5. How do we determine MOLAR MASS? • Molar Mass: Mass in grams of one mole of that substance • What is the molar mass of H2O? 2 Hydrogen atoms: 2 x 1g = 2g 1 Oxygen atom: 1x 16g = 16g 1 mole H2O = 18g • What is the molar mass of CO2? • Fe2O3?

  6. Why is the mole an important unit in chemistry? • Atoms and molecules react with one another particle by particle • The mole is the translation factor between weights and numbers of particles

  7. How do we convert mass to particles? How many moles in 10 g of O2? 10g O2 x 1 mole 32g = 0.3125 mol How many molecules in 55 g of H2O? 55g H2O x 1mole x 6.02 • 1023 18g 1mole = 18.4 • 1023 = 1.84 • 1024 molecules

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